On 20/09/2020 17:29, Oscar Benjamin wrote:
The main difference as far as I tell compared to replace is the need
to create the Wild symbols explicitly. Maybe we could add a bunch of
those to sympy.abc with names like p1_ and p2_ (are those names
standardised?).
Those examples are a revelation! I think they should be added to the
documentation of replace and Wild(). I must admit I thought I'd tried
something like that with replace, but without success - maybe I hit a bug?
Of course I realise that SymPy can't start defining operators like /. ->
etc. In any case, one irritation with Mathematica, is that there are
just too many operator precedences to remember!
The only thing that is standard about the names is the _ on the end, the
rest of the name is chosen by the user, if you named the pattern
variables with a trailing _ in abc , then I think it would be really
friendly - I mean I think a CAS needs to be easy to use.
Given that functionality, the pattern matching looks pretty good. One
other thing is that Mathematica also has a way to define a pattern that
only matches if a predicate returns True when applied to it, for example:
p1_?Even
There are also some more obscure things that can be done with
Mathematica patterns, but probably these are of lesser importance. Also
patterns are used in some other contexts, for example a user defined
function is written with pattern variables as arguments. This allows for
overloaded functions.
It sounds as if the real thing that needs doing is documenting these
features!
I haven't used this at all myself but you might be interested by mathics:
http://mathics.github.io/
""
Mathics is a free, general-purpose online computer algebra system
featuring Mathematica-compatible syntax and functions. It is backed by
highly extensible Python code, relying on SymPy for most mathematical
tasks.
"""
I did consider this, but it became clear that it isn't being actively
supported. For example, it required a specific (out of date) version of
Python. I'd certainly not get anything like the support that your group
offer! Besides, by now, I have got somewhat under the hood of SymPy.
David
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